Sharper imaging in glaucoma focus of $1.85 million NIH grant

January 26th, 2012

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Jason Porter, assistant professor of vision science and biomedical engineering at the University of Houston, stands in front of the AOSLO device he built. Pictured with him are his two graduate students involved in the glaucoma research using the AOSLO, Kevin Ivers (left) and Nripun Sredar (right). Credit: Thomas Campbell

A University of Houston (UH) vision scientist has received a $1.85 million grant from the National Institutes of Health (NIH) to investigate whether his techniques are more effective than others in understanding the earliest changes of glaucoma, which could lead to developing a way to earlier diagnose this potentially blinding disease.

Jason Porter, an assistant professor of vision science and biomedical engineering, uses a state-of-the-art instrument that takes sharper, higher-resolution images of the eye than current clinical instruments. The adaptive optics scanning laser ophthalmoscope, or AOSLO, device Porter uses corrects for the eye's optical imperfections and captures high-resolution movies on a cellular-level in the living eye. Since 2009, his team has been using the AOSLO to image normal and diseased eyes, and the instrument has become a key component of their work in glaucoma, with the goal of using it to better understand retinal diseases.

"Even when wearing glasses or contact lenses, our eyes still have subtle optical imperfections, and these imperfections limit the ability of current clinical instruments to obtain high-resolution images in the eye on a cellular-level," Porter said. "The AOSLO uses a technology called adaptive optics to correct for these subtle imperfections, thereby improving the eye's optical quality and allowing our instrument to capture sharp images of single cells in living eyes. This could potentially lead to more sensitive imaging techniques that may better clarify the causes of glaucoma."

The knowledge resulting from this research, Porter explains, will enhance clinicians' understanding of the development and progression of glaucoma and may provide earlier recognition of structural damage from the disease. The study's results also may result in more sensitive, improved imaging diagnostics used by optometrists and ophthalmologists to prevent vision loss by earlier detecting structural damage to the retina and optic nerve head, as well as help eye doctors to better evaluate and track the effectiveness of glaucoma treatments.

Porter's work concentrates on examining the lamina cribrosa, which is the sponge-like, porous part of the eye in the optic nerve head that provides structural and functional support to the retinal axons as they exit the eye and move to the brain. Signals detected by the retina are transmitted through retinal axons that exit the eye through the optic nerve head and tend to travel in bundles, weaving their way through the pores in the lamina cribrosa and exiting the eye to go to the brain.

Porter says a growing body of research shows that the lamina cribrosa changes in glaucoma, a disease in which pressure may increase in the eye, leading to a bowing and stretching backward of this structure in early stages of the disease. This bowing, he says, could cause changes in the relative geometry of the lamina's pores, potentially damaging the axons coursing through them and, thus, the axons' ability to transport signals to the brain. This damage to the axons results in the loss of ganglion cells in the retina and losses in vision. Porter and his colleagues are interested to see if changes in the lamina cribrosa pores occur before changes in axon loss and vision loss in glaucoma.

"While my lab has expertise in high-resolution imaging of the eye and the lamina, we provide only one piece of the puzzle in glaucoma," Porter said. "It is very important that we relate the changes we see in our images of the lamina cribrosa with other changes that occur in the retina and in a patient's vision. Therefore, our work is really a collaborative effort between several scientists and clinicians in the College of Optometry."

Porter's group works closely with Ronald Harwerth, John and Rebecca Moores Professor and chair of the department of basic sciences, who is a leading expert in how structural changes in the optic nerve head and retina are related to vision loss in glaucoma. They also work in partnership with Laura Frishman, John and Rebecca Moores Professor and associate dean for graduate research, who is a leading expert in the functional changes in vision that occur in the retina and visual pathways in glaucoma, as well as other optic neuropathies. As the study progresses, Porter's team also will collaborate with Danica Marrelli, a clinical professor and optometric glaucoma specialist, who will help recruit normal and glaucomatous patients, as well as interpret the clinical data acquired in these eyes.

Working directly with Porter on lamina cribrosa imaging are two of his graduate students. Kevin Ivers is a Ph.D. candidate in the College of Optometry's vision science and physiological optics graduate program and has developed a great deal of the methodology for imaging the lamina cribrosa using the AOSLO. Nripun Sredar, a Ph.D. computer science student and jointly advised by Porter and professor George Zouridakis in the College of Technology, is developing methods to model the lamina cribrosa in 3-D to improve their understanding of how the lamina pores may change with disease progression.

Provided by University of Houston